Liquid helium is indispensable in most cryogenic studies and for cooling measuring instruments that use superconducting elements. Liquid helium for cooling evaporates and is released to the atmosphere after use in most cases. Liquid helium is a rare resource and is expensive. A strong demand exists to recover and condense evaporated helium gas for reuse.
A recirculation system was recently publicized in which all the helium gas evaporated in the storage tank is recovered and condensed to liquid again after removing the contaminants within the system (Reference 1: Publication of unexamined patent application No. 105072-2000).
That system is, however, unable to prevent gradual intrusion of small amounts of oxygen, nitrogen or other contaminants into the helium gas through various seals in the system. In the helium gas cooling process, these small amounts of oxygen, nitrogen or other contaminants are frozen and attach to various components of the system eventually preventing the system from functioning properly.
To solve these problems, the inventors have already developed a helium gas refiner to remove the contaminants after solidifying them. The helium gas refiner solidifies the contaminants within the refiner while the system is operating. When a preset amount of solid contaminants are accumulated, the contaminants are liquefied by the heaters installed on the refiner for this purpose and the liquefied contaminants are discharged from the refiner system using an appropriate means (Reference 2: Patent application No. 2002-16430).
Contaminants enter the system piping little by little regardless of how tightly the system is sealed. The resultant solids develop in many unforeseeable locations. For these reasons, even if a helium gas refiner with a simply large capacity is produced, occlusion occurs earlier than expected making the unit unusable at some point in time.
Discharging the contaminants from the system after liquefaction means that until then the contaminants must be kept in the liquid phase without evaporation in the refiner. This calls for subtle temperature control of the heaters and involves a complex procedure. It is also a troublesome job to remove the liquefied contaminants from the refiner.
The inventors improved the refiner and developed a new technology to vaporize and purge the solidified contaminants from the system.
This invention described in this document is made based on the above knowledge and it is a circulation type liquid helium recondensation device that can be run for a long time period, in which evaporated helium gas is pumped from the liquid helium storage tank using a circulating pump, refined in the refiner, and liquefied and returned to the liquid helium storage tank for reuse; said refiner is provided with heaters to heat the refiner itself when the amount of the contaminants reaches a preset level to vaporize said contaminants by heat and discharge them to the atmosphere using a pump installed in the device. This invention also is the method of purging the contaminants from said device.
Another objective of this invention is to provide the high thermal gradient helium gas refiner used in the circulation type liquid helium recondensation device to remove contaminants from helium gas and vaporize them to facilitate their discharge from the system.
The other objective of this invention is to provide the transfer tubes used in the circulation type liquid helium recondensation device that feature low heat intrusion from the outside when helium gas is circulating, thereby dramatically improving on energy loss.